A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging the pattern using an ultraviolet (UV) radiation beam onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
It has been proposed to immerse the substrate in the lithographic projection apparatus in a fluid having a relatively high refractive index, e.g., water or a hydrocarbon liquid, so as to fill a space between the final element of the projection system and the substrate. The fluid may be distilled water, although another fluid could be used. The description herein references a liquid. However, another fluid may be suitable, for example, a wetting fluid, an incompressible fluid, and/or a fluid with a higher refractive index than air and desirably a higher refractive index than water. Immersing the substrate into such a liquid enables imaging of smaller features, since the exposure radiation will have a shorter wavelength in the liquid (the effect of the liquid may be regarded as increasing the effective numerical aperture (NA) of the system and increasing the depth of focus). Organic fluids are one of the liquids being considered for use in immersion lithography. These organic fluids have a higher refractive index than water and can include hydrocarbons, such as decahydronaphthalene (also known as decalin), a fluorohydrocarbon, and a cubane dispersed in an organic solvent. Other proposed immersion liquids include, but are not limited to, water with solid particles (e.g., quartz) suspended therein.
Submersing the substrate or substrate and substrate table in a bath of liquid means that there is a large body of liquid that must be accelerated during a scanning exposure. This requires additional or more powerful motors, and the resulting turbulence in the liquid may lead to undesirable and unpredictable effects.
One of the solutions proposed is for a liquid supply system to provide liquid on only a localized area of the substrate and in between the final element of the projection system and the substrate using a liquid confinement system (the substrate generally has a larger surface area than the final element of the projection system).